In a small bowl combine all the marinade ingredients and mix well. Put the chicken breasts in one bowl and the peppers and onions in another. Pour half the marinade over the vegetables and the other half over the chicken. Mix well, cover and refrigerate for 1-2 hours.
Remove the chicken and vegetables from the refrigerator. Prepare your grill for high heat. Grill the chicken on both sides until it has reached an internal temperature of 165 degrees F. Remove from grill, cover and set aside.
Then grill your vegetables until tender - about 10 minutes. If using a traditional grill, I recommend using a grill basket. Toss occasionally.
Wrap your tortillas in a damp paper towel and warm in the microwave to 10 seconds just before serving.
Cut the chicken into strips. To serve, place chicken in a warmed tortilla, top with vegetables and then with you topping of choice.